How to prevent images in Pull Requests being served from camo

I’m trying to serve an image in a pull request from a hosted server at a URL without the image being automatically uploaded and served from camo. I’d like the image to remain being served from the original location.

This is because we are hosting images in a private location and there’s a security risk involved with having the image uploaded and served from camo.

Ie:
![my-private-image](https://www.google.co.uk/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png)

automatically becomes:
![my-private-image](https://camo.githubusercontent.com/asdf1234ghjkl56789qwerty12345…)

I note that in the documentation page entitled: File attachments on issues and pull requests

It mentions the following (emphasis my own):

Warning: If you add an image to a pull request or issue comment, anyone can view the anonymized image URL without authentication, even if the pull request is in a private repository. To keep sensitive images private, serve them from a private network or server that requires authentication.

What I suppose I’m asking is: how do I serve them from a private network as suggested here?